The most accurate method of fitting is with a diagnostic fitting set.
Contact your CLMA member laboratory for fitting set information.
Typically, these lenses are fit like spherical lenses (i.e., often 0.12 - 0.50D flatter than "K").
A spherical over-refraction is performed and the over-refraction is added
to the diagnostic lens powers to obtain the final lens powers.
For example:
- K's: 42.50 @180; 45.50 @ 090
- Refraction: -3.75-3.50 x 180
- (at corneal plane): -3.75-3.00 x 180
- Diagnostic Lens: 42.00/45.00; Plano/-3.00D
- Over-Refraction: -3.25DS 20/20
- Final Order: 42.00/45.00D; -3.25/-6.25D
When there is little to no physiological residual astigmatism,
a spherical over-refraction (as above) will result in good visual acuity;
this lens is termed a spherical power effect or SPE bitoric as it can rotate
on the eye without affecting vision. Photo demonstrates a Good Bitoric fit.
If the patient has significant residual astigmatism, it can be managed by
performing a sphero-cylindrical over-refraction and adding the over-refraction
to the diagnostic lens power per meridian. This lens is often termed a cylinder
power effect or CPE bitoric. If it rotates on the eye, vision may be compromised;
fortunately, this rarely is a problem.
For example:
- K's: 42.50 @ 180; 45.50 @ 090
- Refraction: +1.00 - 4.00 x 180
- Diagnostic Lens: 42.00/45.00D; Plano/-3.00D
- Over-Refraction: +1.50 - 1.00 x 180
- Add: +1.50 to Plano in the 180 Meridian, +0.50 to -3.00D in the 90 Meridian
- Final Order: 42.00/45.00D, +1.50/-2.50D
Go Back to Table of Contents
or
Go to Page 8
